Manufacture of steam-boilers.



D. R. MAGBAIN. MANUFACTURB OP STEAM BOILERS.

APPLICATION FILED HAY 31, 11311.

Patented Sept. 5, 1911.

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. Specification of Letters Patent.

- Patented. sept. 5, 1911.

Application led May 31, 1911. Serial No. 630,439.

Yo all whom it may conce/ra:l

Be it known that I, DONALD R. MACBAIN, of Cleveland, in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in the Manufacture of Steam-Boilers, of which improvement the following is a specification;

My invention relates to steam boilers of the class in which a plurality of tubes is inclosed within a shell or body, more particularly those of the locomotive type, and its object is to provide means whereby the detrimental action of the unequal expansion of the tubes andshell of the boiler will be efcctually counteracted, and the objections resultant upon such unequal expansion be eliminated in 'the operation of the boiler.

In an application for Letters Patent, filed by me January 3,1911, Ser. No. 600,545, ll have set forthan improved method of manufacture of steam boilers, which, generally stated, consists in mechanically imposing a compressive strain upon` the boiler tubes which acts in opposition to the tensional strain imposed upon them in service by the expansion of the boiler shell, and also a tubular steam boiler in which the tubes are subjected to such compressive strain by being secured in tube sheets which are sprung. outwardly, but without permanentset, in the direction of the length of the tubes.

My present invention, which accords inits basic'operative principle and result, With that of my application Ser. No. 600,545, aforesaid, consists in a novel method of imparting initial compressive strain to the tubes of a steam boiler, by springing saidtubes into a' slight longitudinal curvature, and, when so sprung, securing their ends into the tube sheets; also, in a tubular steam boiler' in which are combined two tube sheets, and a plurality of tubes, sprung into slight longitudinal curvature and secured at their ends in said tube sheets.

The improvement claimedv is hereinafter fully set forth.

In the accompanying drawing: Figure 1- engines, and which comprises, as essential elements, a shell or waist, 1, a firebox, 2, atV

the rear end thereof, a smoke box, 3, at the front end thereof, and a plurality of .firev tubes, 4, extending between and secured at their opposite ends to, a rebox tube sheet, 2a, atthe front of the rebdx, and a front tube sheet, 3a, adjoining the rear of the smoke box,

The successful operation, in practical railroad service, of locomotive boilers of the construction above described, particularly whentted with superheater tubes of comparatively large diameter, which are in use A to a considerable extent, has been and is` tireboX temperature and rapid circulation of v water, the expansion of the shell of the boiler, between the tube sheets, is greater than that ofthe tubes, from which unequal expansion there results the exertion of ten-v sile strain on the tubes and their connections to the tube sheets.y If the .tubes were, or

could be, so connected to the front tube sheet as to be capable of slipping therein, that isof moving .longitudinally relatively thereto, without leakage at their joints with the sheet,.the difference of expansion would. be compensated without objectionable results, but as' the tubes are rigidly connected to the front tube sheet, the Atensile strain is eX- erted upon the tube beads at the reboX tube sheet, straining them to such an extent that upon a slight reduction of the temperature of the boiler, leaks will be caused between the tubes and tube sheets. nir/.ed by those familiar with the operation of locomotives, this leakage is a serious objection in serv ice.

Inasmuch as the condition of unequal eX- pansion of the shell and tubes, which is the cause of the leakage of the latter, by irnposing tensilev strain upon them, cannot be prevented, my inventionis designed to prevent its effect upon the tubes from being injurious, by imposing upon them a counteracting strain in the opposite direction, z'. e., one of' compression, and 'thereby instituting a balance of forces which will eliminate the objectionable result produced in steam boil'- ers of the ordinary construction. To this As is well recogend, in the practice of my invention, the

tubes, 4, are, prior to being set in the tube sheets,` 2a, and 3a, sprung into a slight longitudinal curvature, as, into an arc, the versed sine of which may be, in a locomotive boiler others in other directions. 'As shown in thedrawings, the tubes located above the'longitudinal horizontal central plane of the boiler are sprung upwardly, and those'below said' plane are sprung downwardly, but neither this nor any other specific relative: disposi,-- tion of thev curvature of the tubes is an essential of my invention.

The ends of the tubes, when the tubesare sprun out of normal axial line, as above descri ed, are inserted in the holes of the tube sheets, 2*- and 3a, and secured therein, by expanding in the usual manner, and when so connected to the tube sheets, they are, by reasonY of their tendency to resume their normal straight longitudinal direction, subjected to an initial strain of compression.

When, under the intluence of sufficiently high temperature, the expansion of the shell, 1,'exceeds that of the tubes, the tensile strain on the latter, induced by such unequal expansion, is counteracted by the initial compression exerted on .the tubes by 'being sprungl out of line, which compression is relieved in accordance with the expansion of the shell of the boiler. -A

It will be apparent to those skilled in the art, that my invention is applicable, `without departure from its essential and characteristic principle and features, in the manufacture of tubular steam boilers of types which f are structurally differentfrm that which is hereinexemplied, and also that the extent and direction of the curvature of thetubes are matters within the discretion of a competent constructor and may be varied as conditions indicate to be desirable.

I claim as my invention, and desire to -secure by Letters Patent:

1. The improvement in the manufacture of steam boilers which consists in the act of mechanically imposing a compressive strain upon the boiler tubes which opposes the tensile strain imposed upon them in service -under the greater expansion of the boiler shell, by springing the boiler tubes into a slight longitudinal curvature, and, when so sprung, securing their ends into the tube sheets, thereby producing a state or condition in which said tensile strain is compensated and counteracted.

2. The'improvement in the manufacture of steam boilers which consists in the success-ive acts of springing thel boiler tubes into a slight longitudinal curvature, and thereafter mechanically 'imposing a compressive strain upon them by securing their ends, when they are so sprung, in tube sheets, thereby producing a state or condition in which the tensile strain upon the tubes due to the greater expansionl of the shell is compensated and counteracted.

3. .A tubular steam`boiler, the tubes of which are sprung into slight longitudinal curvature, so as to impose upon them, when set, compressive strain in opposition to the tensile strain imposed upon them by the expansion of the boiler shell.

4. A tubular steam boiler,4 the tubes of 'which are Sprung into slight longitudinal sheets'.

DONALD R. MACBAIN. Witnesses:

WJLLIAM F. BOEHRINGER, J. T. PRITCHARD. 

